The aim of this study is to determine the utility of nicotinamide in preventing or delaying the clinical presentation of insulin dependent diabetes mellitus in individuals at an increased risk of developing the disease. Nicotinamide is a water soluble group B vitamin which has been effective in preventing onset of diabetes in animal models, has produced promising results in uncontrolled trials in humans, and may have some benefit in prolonging beta cell function in recently diagnosed patients with insulin dependent diabetes. Within the last year, we have enrolled 15 patients, ages 5 to 40 years, into a randomized, blinded trial to prevent diabetes using nicotinamide (vitamin B3) or placebo. Within the next few months we are planning to enroll 6 more patients. In the state of Texas, there are three more local investigators planning to screen their families with Type I diabetes, and another state is ready to join this International Study. Within the next year, we will begin evaluating the natura history of cellular immunologic events of this disease.